Projectile operating with rocket propulsion



c. D. BURNEY 2,489,953

PROJBCTILES OPERATING WITH ROCKET PROPULSION Nov. 29, 1949 4She'ets-Sheet 1 Filed Sept. 1, 1944 O \N \Q Nov. 29, 1949 c. D. BURNEY 5PROJECTILES OPERATING WITH ROCKET PROPULSION Filed Sept. 1, 1944 4Sheets-Sheet 2 F/GS.

t U41 7 m lpventor {4 MM A Home y Nov. 29, 1949 c. D. BURNEY 2,439,953

PROJECI'ILES OPERATING WITH ROCKET PROPULSION Filed Sept. 1, 1944 4Sheets-Sheet 3 In venlor MAM M, j M

A ltorney Nov. 29, 1949 c. D. BURNEY PROJECTILES OPERATING WITH ROCKETPROPULSION 4 Sheets-Sheet 4 Filed Sept. 1, 1944 T ER .mv MM NW Wm WW I m2. W. T F u ///////V u G II 9 I I.

: 1 n--- e i! 1| I on, K N\,w\|.\ G 3 W0 T E m m m W 4 I I A Home y ByidPatented Nov. 29, 1949 rnoeunsron Charles Dennistoun Burney, BaynardsPark, near Cranleigh, England Application September 1, 1944, Serial No.552,346 In Great Britain September 4, 1940 Section 1, Public Law 690,August 8, 1946 Patent expires September 4, 1960 Claims.

The present invention relates mainly to rocket projectiles, by which ismeant projectiles whose velocity is increased after they leave the gunmuzzle, by means of the thrust produced by the reaction on the air ofgases discharged rearwardly from the projectile, said gases beingdeveloped by the combustion of a propellant charge within the body ofthe projectile. Such projectiles are necessarily of greater length thannormal in reiation to their calibre, so that they are of increasedinternal volume. Since the extra length of the projectile will increaseits weight, the ballistic coeflicient of the projectile will beincreased, and thus when fired at the same velocity as an orthodoxprojectile its range will also be increased, apart from such advantagesin performance as may be gained by the effective utilisation of theincreased volume of the projectile for rocket propulsion.

Considerations of stability normally impose restrictions on thepermissible length of a projectile in relation to its calibre, inasmuchas it is essential for stability to maintain the centre of gravity asclose as possible to the centre of pressure, which is fixed for a givencalibre of projectile by the frontal aspect of the projectile. On theother hand any increase in the length of a normally constructedprojectile adds very materially to the weight of its rear portion, sinceits walls have to be sufliciently thick at all points along their lengthto carry the accelerating forces for the forward part of the projectile.Thus it is common practice in the design of ordinary shells forvthethickness of the wall to be graded from a minimum at the nose end to amaximum at the base end, since the accelerating forces will graduallydecrease from the base to the nose of the projectile.

The main object of the present invention is to provide an improvedconstruction of rocket projectile of such increased length as to provideadditional internal volume to carry a rocket propelling chargeadditional to the normal explosive charge, so that the advantages ofrocket propulsion are not obtained at the expense of the tactical valueof the projectile. In other words, it is desired to increase the volumeof the projectile so that it can contain an adequate rocket chargewithout reduction of its stability.

ternal pressures when the projectile is fired from the gun. Thus thepropelling force of the excasing by combustion of a suitable charge inthe projectile. Thus, in the first case, one or more openings to theinterior of the casing may be provided in rear of the driving band orgas check, which place it into communication with the chamber of thegun, so that on explosion the chamber pressureimmediately becomeseffective in the interior of the casing. The communic t on between thecasing and the gun chamber may be provided by one or more of the nozzlesprovided for the escape of the gases developed by the rocket charge andused after the projectile has left the gun muzzle to produce propulsr'ereaction.

The main invention is therefore characterised by two important features,firstly, the weight of the projectile is graduated steeply from thedriving band to the rear, so that the centre of gravity lies as farforward as possible, and secondly, the propulsive force of the explosionin the gun is applied, not to the rear end or base of the projectile,but to a plane intermediate along its length and as close to the drivingband or gas check as possible, in consequence of which the forward partof the projectile is driven by the force of the explosion, whilst therear part of the projectile is towed by the forward portion. Thusinconstructing the projectile the walls of the forward portion or mainbody portion of the projectile may be graded or gradually reduced inthickness forwardly of the driving band in known manner, whilst thewalls of the casing extending rearwardly from the driving band may notonly be relatively thin but may even be graded, or gradually reduced inthickness in the rearward direction, thereby still further contributingtowards a forward position of the centre of gravity of the projectile asa whole.

The rear portion of the projectile may be cylindrical in shape and ofsubstantially the same diameter as the forward or main body portion, butin some cases it is preferably tapered in the 3 rearward direction so asto be of substantially stream-line form.

In the case of rocket propelled projectiles. the production of a uniformreaction thrust is of great importance, and this depends to a great extent on the nature of the rocket charge and on factors which affect itsrate of combustion. It is natural, for example, that the rate ofdevelopment of gases will depend upon the burning area of the rocketcharge, and when a solid combustible, such as cordite, is used, it iswell-known that in order to produce uniformity in the buming area it isnecessary to employ tubular cordite, which burns on both the inner andouter surfaces, so that the decrease in the outside burning area will becompensated by the increase in the internal burning area.

Furthermore, it has been found in the case of cordite, for example, thatit is productive of gases at different rates depending upon the varyingconditions of temperature and pressure to which it is subjected. Ifcordite is used as the rocket propellant in a rocket projectile, whereit operates in a chamber which is closed except for the gas dischargenozzles, it is found that a small varia-- tion in the nozzle area makesa considerable difference in the internal pressure. If the pressurefalls, the rate of burning of the charge falls, so that the pressurefalls still further, and finally the pressure becomes so reduced thatburning ceases. On the other hand if the pressure increases it continuesto rise until a point is reached when the remaining rocket chargeexplodes instead of continuing to burn at a steady rate.

For accuracy of shooting with rocket propelled projectiles, it is ofgreat importance to maintain, a steady reaction thrust and to avoidextinction of the combustion on the one hand, and bursting of the rocketcharge casing on the other hand. Consequently, although the eifect ofvariations in temperature may generally be neglected it is highlyimportant to provide means to maintain a constant internal pressurewithin the rocket charge casing, as has been heretofore proposed inconnection with ordinary war rockets.

It has been proposed to obtain the desired result in the case of warrockets by discharging the gases through an annular nozzle having a wallwhich expands under increase of pressure so as to increase the nozzlearea and maintain the area. proportional to the pressures within'theelastic limit of the wall. According to its invention, however, one ormore of the gas discharge nozzles is or are fitted with an automaticvalve which floats under spring control in the nozzle opening andregulates its effective size in accordance with the pressure of thegases in the rocket casing. The valve may consist, for example, of aconical valve body located in the throat of the nozzle and adapted to bemoved against spring resistance to increase the effective nozzleopening, by the pressure acting on the valve. Alternatively, in the caseof the gases discharging through a number of apertures or nozzles, oneor more apertures or nozzles or an additional axial hole or nozzle maybe fitted with a poppet valve which is opened by the gas pressureagainst spring resistance. If it is desired to make allowance forvariation in temperature conditions, provision may be made for varyingthe initial compression of the control spring, as by providing anadjustable screw abutment for the end of the spring, the adjustmenttemperatures.

aeaaesa I when cordite is used as the rocket charge. if in long lengthsit is liable to break up due to the acceleration forces arising from itsown weight, with consequent increase of burning surface, too rapidevolution of gases, and possible bursting of the rocket casing. To avoidthis source of uncertainty and irregularity of action, according to afurther feature of the invention the cordite is sub-divided into lengthswhich are liable to stand the acceleration forces, perforated supportingplates or grids being interposed between the lengths.

Another important factor in obtaining uniformity of rocket thrust andthe maintenance of such thrust fora predetermined period of time is theprovision of satisfactory means for ensuring complete combustion of therocket charge and the prevention of loss of rocket charge in the form ofsolid unburnt particles of charge carried away with the gases. Part ofthis invention resides in the provision of such means, and according toone feature of this part of the invention the gases pass to thedischarge nozzles along an extended path so that solid particles aregiven time to ignite before reaching the nozzles. Preferably thedirection of motion of the gases is reversed in passing to the nozzlesso that the momentum of the solid particles stops their continued motionafter the reversal point. According to another method the gases arecaused to travel along a circular path so that they not only travelalong an extended path but also become subject to the action ofcentrifugal force which throws the solid particles outwards and awayfrom the direction of the continued travel of the ases.

In order that the invention may be more clearly understood and readilycarried into practice, examples of projectiles embodying the variousfeatures of the invention will now be described Figure 4 illustrates apressure control valve applied to the nozzle system illustrated byFigure 2,

Figures 5 and 6 are sectional views of gas discharge nozzles embodyingmeans for cleaning the gases from solidparticles before discharge,

Figure 7 is a longitudinal section of another construction of rocketprojectile according to the invention,

Figures 8 and 9 are cross-sectional views on the lines VIIIV'III andIX--IX of Figure '7,

Figures 10 and 11 are longitudinal sectional views of fixed ammunitionfor small arms and quick-firing field guns respectively, embodyingthe'invention,

Figure 12 is a longitudinal section illustrating the application of agun muzzle extension, to the muzzle of a gun to adapt it to fireself-propelled projectiles according to the invention, although thisconstruction forms no part of the present invention,

Figure 13 is an end view of the extension, and Figure 14 iscross-section on line XVII-,XVII of Figure 12.

The constructional example shown in Figure l is a shell having a normalmain body portion I, containing the usual explosivecharge and fuzemechanism and fitted with a normal driving band 2. Rearwardly from thedriving band 2 extends a relatively thin walled casing 3 in which iscontained a rocket charge 4 consisting of a tube of cordite, supportedby a perforated plate 5 which is engaged against a shoulder in the 08S.ing 3. This perforated plate 5 serves not only to hold the corditecharge in place but, also to prevent the passage of solid particles ofthe burning charge to the discharge nozzle. The plate 5 therefore actsin a measure as a gas cleaning device.

In the end of the casing 3 is screwed a hollow nozzle cap 6 comprising acentral tubular member I, which is shouldered to support the centre ofthe disc 5, and the bore of which communicates at 8 with the interior ofcasing 3.. In the wall of member I are a number of radial holes 9providing communication between the central tubular member I and thesurrounding annular space Ill. At the bottom of the annular space i0,and through the end wall of member 6, are.

formed an annular series of nozzles ll of Venturi form, through whichthe gases evolved by the combustion of charge 4 escape into theatmosphere, and in doing so provide propulsive reaction for theprojectile, which supplements the velocity imparted to the projectile bythe gun from which it is fired. These nozzles H may discharge indirections parallel to the axis of the projectile but preferably theyare all inclined at an angle to the axis of the projectile so as to giverise to a reaction having a tangential or peripheral component, wherebypart of the energy of the gas reaction is utilised in spinning theprojectile about its axis so as to maintain I the necessary stabilisingspin after the spin imparted by th riding of the gun has ceased to beeflective.

Figure 2 illustrates a modification in regard to the nozzle system,according to which instead of discharging through a ring of annularnozzles H, the reaction gases discharge through a single axial nozzlel2. In this case the nozzle cap 6 again has a central tubular member I,with lateral openings 9, which supports the perforated disc 5 holdingthe rocket charge 4 in position. For axially spinning this projectile bygas reaction, supplementary to the spin imparted by the riiiing of thegun through the intermediary of driving band 2, an annular series ofinclined nozzles may be provided just in rear of the driving band asdescribed subsequently in connection with Figure 7.

In order to avoid the possibility of the projectile becoming unbalancedwhen the rocket charge is partially burnt, and is thus sufiicientlyreduced in diameter to take up an eccentric position in casing 3, theexpedient illustrated by Figure3 may be adopted. In this case thecordite charge is divided into four tubular sections l3, which areseparated from one another by one or more metal separators M which arestarshaped in cross-section. As the sections l3 become burnt at equalrates and are maintained by the separator or separators I4 symmetricallyin relation to the'axis of the projectile, the balance of the projectilewill remain unalteredas the rocketcharge burns.

Figure 4 illustrates how a pressure regulating valve may be embodied inthe example illustrated by Figure 2. Within the nozzle 12 is supportedby spider arms IS, a tubular member l5 containing a compression springI! surrounding the rod l8 of a conically headed valve [9 which islocated in the throat of the nozzle i2. The

V 6 rod It carries a collar 20 against which the inner end of spring I!bears, and on the end of the tubular member 6 is a screw cap 2| againstwhich the outer end of the spring bears, and byrotation of which theinitial tension of the spring I! can be adjusted. The outside of thetube It may be graduated so that the cap 2| can be adjusted to give aninitial tension suited to the prevailing temperature conditions. As thegases issue from the nozzle l2 they exert pressure on the valve l9,which if too great overcomes the spring I! and moves the valve l9outwardly, thus increasing the annular space for the passage of thegases through the nozzle l2 and lowering the pressure inside thecontainer 3. If, on the other hand, the

pressure inside the container 3 falls below the desired value, the valvei9 will move forwardly into the throat of nozzle l2 and thus restrictthe efifective nozzle area, whereby the pressure in the container 3 willrise. In practice the valve is will float in a position maintainingsubstantially constant pressure within the container 3, so that thereaction thrust which propels the projectile remains substantiallyconstant.

Figure 5 illustrates a construction of nozzle fitting embodying meansadditional to the perforated plate 5 for cleaning the gases morethoroughly from unburnt particles of combustible before discharge, asapplied to a single axial nozzle, such as that of Figure 2. The internaltubular member I is formed with a helical vane or bafiie 8| which doesnot extend quite to. the wall of the nozzle fitting 6, whilst betweenthe convolutions of the balile 4i holes 42 are formed through themember 1. The gases are prevented from passing straight through themember i to the nozzle i2 by means of an internal crosswall or partition43, which forces the gases to pass round the convolutions of the helicalbaffle 8|. This rotary motion of the gases gives rise to centrifugalforce acting on the solid particles carried along by the gases, whichthrows them out radially against the wall of the nozzle fitting 6. Atthe same time the gases traverse a sinuous path which increases theirtime of passage to the nozzle l2 and gives more time for the solidparticles to become burnt.

Figure 6 illustrates another method for cleaning the ases, according towhich the rocket charge is supported at the rear end by a solid plate 40which prevents direct access of the gases to the nozzles l I and forcesthem to travel forwardly through the front perforated supporting plate4| and thence into the central passage 44,

along which is disposed a helically twisted strip of metal 45 whichimparts a rotary motion to the gases as they pass alon the passage, tothe mixing chamber 46, formed by a perforated cage 61, which serves tohold back solid particles of combustible within the chamber 45.

Thus a proportion of the gases in passing to the nozzles I! are forcedto travel along an extended path and are reversed in their direction ofmotion after passing through perforated plate ll, whilst all of thegases are given a spiral rotary motion by the spiral strip 45, so thatsolid particles are thrown outwardly by centrifugal force and retainedeither in the central passage, or in the mixing chamber 46, until theyhave become ignited and converted into gas.

Figure 7 illustrates a modified construction for a rocket projectilewhich is required to contain a considerable quantity of propellant byreason of the high maximum velocity and range desired, and by reason ofthe small calibre of accuse the projectile it is necessary for thepropellant space in the projectile to be very elongated.

'When the propellant is cordlte it is found that definite limits areimposed on the permissible length of the cordite strands or tubes,having regard to the acceleration forces which they have to carryarising from their own weight, and accordingly as shown, the cordite issub-divided in length into two charges 4a and lb loaded one behind theother with an intermediate periorated supporting plate 5.

The rocket charge casing comprises a cylindrical section 22 into whichis screwed a tapering section 23, the end of which supports theperforated plate 5, and on the other end of which is secured a conicalnozzle member 24, so that the rear part of the projectile issubstantially of streamline form.

The. cylindrical casing 22 may have its wall graded or reduced inthickness rearwar'dly from the driving band 2, and the wall of theforward or main body portion of the projectile may be graded or reducedin thickness in the reverse direction, i. e. forwardly of the drivingband 2, as is the common practice with shells.

- As already explained the rocket charge is subdivided into two parts 4aand 4b of suitable length contained respectively in the two cases 22 and23. The forward part of rear casing 23 is externally shouldered at 25,and'an annular series of nozzle openings 26 are formed therewith, in anangular direction in relation to the axis of the projectile and facingrearwardly, so as to give rise not only to a propulsive thrust but alsoto a peripheral or spin imparting reaction. At the rear end 01 thecasing 23 is an axial nozzle fitting 21, which is covered over by theconical tail piece 2E, having outwardly inclined nozzle openings 28producing an axial thrust and also if desired inclined to the axis togive a peripheral reaction productive oi spin. The nozzle 21 is fittedwith a pressure control valve 23 in the form of a poppet valve, the stem01' which moves in a bore in the tail fittin 24 under the control of aspring 30, the initial tension of which may be adjusted to suittemperature conditions by a finger screw member 3|, having a springfinger 32 co-operating with calibrated notches in the tail piece 24.

It will be understood that in the constructions oi. projectiledescribed, the rocket charge 4, or 4a and 4b, will be ignited by theflash of the explosion in the chamber of the gun, and that the nature ofthe rocket charge and its. rate of burning will be chosen according tothe desired magnitude and duration of the rocket thrust. It will also beunderstood that it the nozzle openings communicating with the chamberspace are insulficient in area to allow immediate equalisation of thepressure inside and outside the casing 3 (22, 23) on explosion of thegun charge, a part of the normal rocket charge will be replaced by acharge having the same rate of burning and pressure development as thegun charge, so that an internal pressure de- 05 gun. It a cartridge caseof normal size is employed the propelling charge will be reduced involume and thus the muzzle velocity will be reduced. The recoil willalso be reduced, so that if the small arm is of automatic or machine guntype the recoil mechanism and th mounting may be of lighter than normalconstruction. If, however, it is desired to obtain the normal muzzlevelocity the cartridge case 36 must be enlarged in diameter, or length,or both, to compensate for the space occupied within the cartridge bythe rear end extension of the bullet, carrying the rocket charge intothe casing, and to allow also for the extra weight of the projectile.

If, however, it is only desired to obtain a maximum velocity equal tothe normal maximum velocity, i. e. the -normal muzzle velocity, and torely for greater range on the improved ballistic coefilcient of thebullet due to its extra weight, the increase in the-volume of thecartridge case will be somewhat less, and will depend upon theproportions of the maximum velocity to be attributed respectively to thegun and to the rocket charge. Since the rocket tail of the projectilewill occupy a substantial proportion of the cartridge space availablefor the propellant charge, the volume of the cartridge case must beincreased if the normal muzzle velocity is to be attained, either byincreasing its diameter or its length, or both. If, however, it isdesired to operate with a sub-normal chamber pressure it may be possibleto use a cartridge case of normal size.

A fixed type of ammunition, suitable for use with a light quick-firingfield gun is illustrated by Figure 11. The construction is similar tothat of Figure 10, but the projectile I itself is shown of the typeillustrated by Figure 1, and the mouth of the cartridge casing 31 iscrimped at 38 to engage in a groove round the projectile in rear of thedriving band 2. As in the case of small arm ammunition a cartridge case31 of normal size will result in a sub-normal muzzle velocity due to thereduced space available for the propellant charge in order toaccommodate the rocket charge casing 3, and therefore to obtain thenormal muzzle velocity the volume of the cartridge case 31 will requireto be suitably increased.

Since normal guns cannot be used for firing rocket or other projectilesaccording tothis invention, in order that this specification may besufllcient to enable the invention to be carried into practice, certainnovel features of construction', or modifications in the construction ofguns are necessary, which, however, form no part of the presentinvention, will now b described. It should be noted that owing to theincreased weight of the projectile due to the added propellant charge,and to the limitations imposed on the chamber pressure, the accelerationof the projectile will be slower and therefore a slower burningpropellant charge may be used in the In the first place the rifiingpitch normal to a gun of given calibre will not be suited to projectilesof the extended length forming the subject matter of this invention, andin consequence, with normal muzzle velocity, it becomes necessary toincrease the pitch of the rlfiing in order to increase the rate of spinimparted by the gun to the projectile to produce stability immediatelythe projectile leaves the gun muzzle. Thus a measure of overspin isgiven in comparison with y 78 normal practice.

Further the volume, and thus the dimensions of, the gun chamber, willrequire modification in comparison with standard practice, dependingupon the tactical performance required of the gun. Assuming for themoment that it is required simply to increase the maximum velocity ofthe projectile to give greater range and/or penetration powers, whilstretaining the normal muzzle velocity, then the rearward extension of theprojectile into the chamber of the gun will reduce the space normallyavailable for the propolling charge, in consequence of which the chamberwill require to be increased in volume, it the same propelling charge isto be used, by the volume which the propellant casing of the projectileoccupies in the chamber when the projectile is in firing position.Standard guns of calibre appropriate to the projectile may be modifledto increase the chamber volume by removing or eliminating a suitablelength of the rifling of the barrel towards the chamber so that thedriving band seating is shifted so far forwardly'that the rocket chargecasing is wholly or partly accommodated in the bore of the gun.

In other words the combustion chamber volume is enlarged by including init a portion of the barrel volume. If the rocket charge casing is ofless diameter than the bore the surrounding annular space should beregarded as part of the chamber volume, so that in that case a volume ofthe casing may be left within the chamber equal to the volume of saidannular space. Consequently, the rocket charge casing may project onlypartly into the chamber proper. If, however, the rocket charge casing isa close fit in the bore of the gun, the whole of'its length must beaccommodated in the bore of the gun so that it does not reduce theeffectiv chamber .volume.

New guns may be constructed with an advanced band seating, but, sincethe effective length of the barrel is reduced by accommodating theprojectile wholly or partly in the barrel before firing, new guns arepreferably constructed so that the efiective length of barrel is notreduced, specifically for use with rocket propelled projectiles. Theband seating will be located where the rifiing meets the chamber, andtheincreased chamber volume required to compensate for the presence of therocket charge casing within the chamber will be provided by increasingthe diameter and/or length of chamber volume required to compensate forthe. presence of the rocket charge casing within the chamber will beprovided by increasing the diameter and/or length of the chamber proper.Since the chumber pressure will thus be maintained of normal value thestrength and thickness of the chamber walls will not require to beincreased. Consequently the weight of the gun will not require to besubstantially increased, since only a relatively small increase ofweight will follow from the increased diameter and/or length of chamber.

Thus whereas in the case of a standard gun of given calibre the chambervolume bears a definite relation to the volume of the propelling chargeto be fired therein for maximum range, in

guns for firing projectiles according to this invention, the chambervolume will be increased in relation to the normal ratio by an amountequal to the volume of the chamber space occupied by the propellantcharge casing of the projectile, when in firing position in the gun.

. increase of the chamber volume.

the gun and wholly accommodated before firing.

in the chamber, then, in order to maintain the same eflective or netchamber volume, the gross chamber volume will require to be increased bysome 40%, so that the gun propellant charge will only then occupy 28.5%of the gross chamber volume, or conversely, instead of the gross chambervolume being 2 times the volume of the propellant charge, it will be 3times the volume of the propellant charge.

In applying the invention to fixed ammunition for quick firing guns thecartridge case will be treated as the equivalent of the gun chamber. Inother words, its diameter or length will be increased in order that thecase may receive the rocket propellant casing of the projectile withoutdecrease of the volume normally provided for the explosive propellantcharge contained in the case. The gun chamber will of course have to becorrespondingly increased in diameter or length to receive the enlargedcartridge case.

Similar considerations will apply when for tactical reasons no increaseof maximum velocity is required to give greater range and/or penetrationpowers, the advantages of lightness of gun construction, increasedmobility, and reduction of barrel wear being the desiderata. In thiscase the reduction of the gun propellant volume arising from theoccupation of part of the chamber space by the rocket charge casing, mayonly require to be made good to a partial extent, by

In this connection allowance will have to be made for the increasedweight of the projectile necessitating a larger charge for a givenmuzzle velocity thanv for a projectile of the same calibre but normallength, and allowance must also be made for the fact that the rocketcharge will operate with less eficiency than that of the gun chamberpropellant in producing velocity.

As hereinbefore briefly indicated it has been found in practice thatlong projectiles, such as projectiles according to this invention, aresubject to fortuitous inaccuraclties which appear to be due to themuzzle blast of the gun acting on the base of the projectile immediatelyafter it has left the muzzle and before the blast has had time todissipate. Any slight axial deviation of the projectile on leaving themuzzle produces, owingto the great length of the projectile, arelatively large angular cant of the base of the projectile, with theresult that the muzzle blast acting on the canted base is liable to givethe projectile a powerful lateral thrust which magnifies the deviationto an undesirable extent. To overcome this difiiculty, the expedientillustrated by Figures 12-14 may be adopted. These figures illustrate ameans for reducing muzzle blast applicable to existing guns, accordingto which the muzzle end of the gun 48 is reduced and threaded externallyat 49 to receive the socket end 50 of a barrel extension 5|. Thisextension 5| is of the same diameter as the bore of the gun barrelacross the lands, but has no rifiing, and at intervals along its lengthit has rings of gas vents 52, which allow the escape of the explosiongases as soon as the base of the projectile passes them, so that by thetime the base of the projectile leaves the mouth of the muzzle extension5|, the force or blast of the gases issuing from the Assuming apropellant cartridge charge equal bore itself is reduced to a valuewhich is not adverse in its efi'ect on the base oi the projectile in themanner described above.

Preferably the muzzle extension ii is enclosed by a tubular casing 53spaced from the muzzle extension to provide an annular space 54 for thepassage of the gases as indicated by the arrows, which will produce atubular blast surrounding the base of the projectile and tending toresist any lateral deviation of its base end, a direct blast on the baseof the projectile being mainly or wholly eliminated. In order to providefor the fitting of the tubular casing 53, the extension 5| has a doubleshouldering at 55, the outer one of which receives the end of the casing53, and the inner one produces the annular space At its forward end thecasing 53 is supported from the mouth end of the muzzle extension 5| bya number of radial screw bolts 56. Whilst Figures 12-14 show anattachment suitable for application to existing guns modified in asuitable manner, it will be understood that new guns may, if desired, beconstructed in a corresponding manner, the muzzle extension 5| beingmade integral with the normal gun barrel and the socket 50 beingeliminated.

It should be understood that the improved projectiles may be desired foruse not only with heavy ordnance, such as artillery and naval guns ofall calibres, but also for use with small arms such as rifles, machineguns, and anti-tank guns.

Further, although several constructions of projectile and constructionalmodifications have been described, it should be understood that many ofthe constructional details are interchangeable so that the inventionshould not be regarded as restricted to the constructional examplesshown, many other modifications and constructional forms being includedwithin the scope of the invention.

What I claim is:

1. A self-propelling projectile of the type adapted to be fired from thechamber of a gun by an explosive propellant charge including incombination with the body proper of the projectile, a thin walled casingextending from the base end of said body, a self-propelling rocketcharge contained in said casing, means associated with said casing forproviding communication between its interior and the propellantchargechamber from which it is fired, said last named means being constructedto provide, upon firing, a substantial equalization of thepressureinternally of said casing with the chamber pressure actingexternally thereon, and means associated with said casing whereby solidunburnt particles are separated from the gases arising from combustionof the rocket charge.

2. A self-propelling projectile of the type adapted to be fired from thechamber of a gun by an explosive propellant charge including incombination with the bodyproper of the projectile, a thin walled casingextending from the base end of said body, a self-propelling rocketcharge contained in said casing, means associated with said casing forproviding communication between its interior and the propellant-chargechamber from which it is fired, said last named means being constructedto provide, upon firing, a substantial equalization of the pressureinternally of said casing with the chamber pressure acting externallythereon and including at least one expansion nozzle through which thegases produced by the continued burning of said rocket charge aredischarged rearwardly to produce a propelling reaction on saidprojectile, and at least one perforated plate disposed between saidrocket charge and said nozzle.

3. A self-propelling projectile of the type named means beingconstructed to provide, upon. firing, a substantial equalization of thepressureinternally of said casing with the chamber pressure actingexternally thereon, and means associated with said casing whereby solidunburnt. particles are separated from the gases arising from combustionof the rocket charge and including means for reversing the direction ofmotion of said gases.

4. A self-propelling projectile of the type adapted to be fired from thechamber of a gun by an explosive propellant charge including incombination, with the body proper of the projectile, a thin walledcasing extending from the base end of said body, a self-propellingrocket charge contained in said casing, means associated with saidcasing for providing communication between its interior and thepropellantcharge chamber from which it is fired, said last named meansbeing constructed to provide, upon firing, a substantial equalization ofthe pressure internally of said casing with the chamber pressure actingexternally thereon, and means associated with said casing whereby solidunburnt particles are separated from the gases, arising from combustionof the rocket charge and including means for imparting a rotary motionto said ases.

5. A self-propelling projectile of the type adapted to be fired from thechamber of a gun by an explosive propellant charge including incombination with the body proper of the projec-' tile, a thin walledcasing extending from the base end of said body, a self-propellingrocket charge contained in said casing, means associated with saidcasing for providing communication between its interior and thepropellant-charge chamber from which it is fired, said last named meansbeing constructed to provide, upon firing, a substantial equalization ofthe pressure internally of said casing with the chamber pressure actingexternally thereon, and means associated with said casing whereby solidunburnt particles are separated from the gases arising from combustionof the rocket charge" and including means forming a helical path alongwhich at least some of said gases must fiow.

6. A self-propelling projectile of the type adapted to be fired from thechamber of a gun by an explosive propellant charge including incombination with the body proper of the projectile, a thin walled casingextending from the base end of said body, a self-propelling rocketcharge contained in said casing, and means associated with said casingfor providing communication between its interior and thepropellant-charge chamber from which it is fired, said last named meansbeing constructed to provide, upon firing, a substantial equalization ofthe pressure internally of said casing with the chamber pressure actingexternally thereon and said rocket charge comprising a plurality ofcylindrical sections disposed symmetrically in said casing.

7. A self-propelling projectile oi the type adapted to be fired from thechamber of a gun by an explosive propellant charge including incombination with the body proper of the projectile, a thin walled casingextending from the base end of said body, a self-propelling rocketcharge contained in said casing, means associated with said casing forproviding communication between its interior and the propellantchargechamber from which it is fired, said last named means being constructedto provide, upon firing, a substantial equalization of the pressureinternally of said casing with the chamber pressure acting externallythereon, and means associated with said last named means for maintain- Winga substantially constant pressurein said casing.

8. A self-propelling projectile of the type adapted to be fired from thechamber of a gun by an explosive propellant charge including incombination with the body proper of the projectile, a thin walled casingextending from the base end of said body, a self-propelling rocketcharge contained in said casing, means associated with said casing forproviding communication between its interior and the propellant-chargechamber from which it is fired, said last named means being constructedto provide, upon firing, a substantial equalization of the pressureinternally of said casing with the chamber pressure acting externallythereon, and means associated with said last named means for maintaininga substantially constant pressure in said casing, said last named meansincluding a valve for closing an aperture through which flow the gasesarising from the combustion of said rocket charge and a spring forurging said valve in a direction to restrict said aperture upon decreaseof gas pressure in said casing.

9. A self-propelling projectile of the type adapted to be fired from thechamber of a gun by an explosive propellant charge including incombination with the body proper oi the proiectile, a thin walled casingextending from the base end of said body, a self-propelling rocketcharge contained in said casing, means associated with said casing forproviding communication between its interior and the propellantchargechamber from which it is fired, said last named means being constructedto provide, upon firing, a substantial equalization of the pressureinternally of said casing with the chamber pressure acting externallythereon, said rocket charge being subdivided in the direction of thelength of the projectile, and means separately supporting saidsubdivisions.

10. In a rocket-propelled device having a propelling rocket charge and acasing surrounding said charge, said casing having an open end throughwhich the gases resulting from the burning of the charge exhaust to theatmosphere, concentric outer and inner elements disposed within saidopen end and being contoured to form an open Venturi passagetherebetween in all positionsoi' said elements, for said gases,said'innei' element being movable axially of the outer element to varythe size of said passage, and means for maintaining said inner elementin predetermined position, and providing the said open Venturi passageat normal and sub-normal pressures developed within said casing andbeing operative in response to abnormal pressures within said casing topermit said inner element to enlarge said passage.

CHARLES DENNISTOUN BURNEY.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number 7 Name Date 328,919 Chambers Oct. 27, 1885785,644 Unge Mar. 21, 1905 976,732 Gherassimoff Nov. 22, 1910 1,141,042Davis May 25, 1915 1,633,710 Newton June 28, 1927 1,901,852 Stolfa etal. Mar. 14. 1933 2,005,913 Cofiman June 25, 1935 FOREIGN PA'IENTBNumber Country Date 2,497 Great Britain Nov. 8, 1858 54,100 France May7, 1862 1,734 Great Britain Apr. 24, 1878 25,945 Great Britain Nov. 17,1896 831,487 France June I, 1988 516,865 Great Britain Jan. 12,1940

